Electroacoustic device



Patented July 30, 1935 UNITED sTATEs PATENT OFFICE Application January 18, 1934, Serial No. 707,190

In Germany June 29, 1933 f Claims.

` condenser type, for example, is increased to such an extent that the electric connection with the associated amplifying apparatus can be effected "without taking into consideration the length of the' conductors between the microphone and the amplifier. The invention may also be applied advantageously to sound reproducers of the condenser type.

, In apparatus of the character described, according to the invention, a dielectric is employed comprising a fluid having a high dielectric constant. The fluid is preferably absorbed in a suitable medium or vehicle, for example, of paper or the like. If the microphone 'or reproducer comprises an arrangement in which the diaphragm engages or rests upon a perforated stationary metal electrode, as in the construction shown in,

my German Patent No. 455,151 or U. S. Patent No. 1,859,170, a thin coating of collodion, celluloid or the like is preferably provided to Aprevent the vehicle from adhering to the electrode.A

For a better understanding of the invention, reference should be had to the accompanying drawing, wherein Fig. 1 is a. fragmentary view in cross section of a microphone or reproducer of the condenser type embodying the invention; and

Figs. 2 and 3 are circuit diagrams illustrating applications of the invention.

As shown in Fig, 1, the invention is embodied in the diaphragm of a microphone, telephone receiver or loudspeaker of the condenser type. The diaphragm comprises an extremely thin coating I of collodion, celluloid or the like on a disc or sheet 2 of paper or the like impregnated with a fluid of high dielectric constant, the disc or sheet 2 having an extremely thin conducting covering or coating 3, preferably of metal foil. The disc 2 may be impregnated with a liquid, such as Water Aor glycerin, the dielectric constants of which are 80 and 40 times greater than air, respectively. The layer 3 may consist, for example, of aluminium or gold foil.

The' purpose of the coating I is to prevent the moist paper from adhering to the perforated metal electrode 4. On the other hand, the outer coating I is strongly damped by the paper di'sc 2 so that it is unnecessary to damp the air vibrations in the passages in theelectrode 4 to a great extent; that is, the lower ends of the passages need not be completely closed. It has been demonstrated in actual practice that, by constructing the diaphragm as described above, the electrostatic capacity may be increased 10G-fold as compared with prior apparatus of the same size.

In Fig. 2 is shown,.by way of example, a circuit in which a microphone 5 embodying the invention is connected to an amplifier. AThe terminals of the microphone 5 are connected to an auto-transformer 6 having a condenser 'l connected between the windings thereof. The transformer 6 is connected to the amplifier by conductors 8 through which current is supplied to the microphone'from a battery 9. Resistors I 0 of high ohmic resistance are connected to the terminals of the battery 9 and in series relation with the primary windings of an'input transformer I I of the amplifier, the secondary windingof the input transformer being connected to an amplifier tube I2 in the usual manner. A condenser I1 is connected between the primary windings of a the transformer II in shunt relation with the battery 9. A microphone constructed in accordance with the invention is particularly suitable for use in 4a system of this kind because its high electrostatic capacity minimizes the `effect of variations in the length of the conductors 8 between the microphone and the amplifier.

The invention is also of value in systems where the improved apparatus is used as a telephone receiver or loudspeaker. Such a system is illustrated in Fig. 3 where the reproducer I3 is energized through the anode resistance I4 from a battery I5 and is connected in the output circuit of the iinal amplifier tube I6 of a conventional amplifier.

It is to be noted that the microphone or telephone need not be directly connected with the associated amplifier as the great capacity thereof makes it possible to use a transformer which permits the impedance of the microphone or telephone to be transformed to any desired value.

I claim:

1. An acoustic device of the condenser type comprising a stationary elctrode and a dia- 50 phragm having a conducting aluminium foil, an Aabsorbent layer impregnated with glycerine, and

a layer of Celluloid adjacent the electrode.

2. An acoustic device of the condenser type comprising a stationary electrode and a diaphragm having a conducting gold foil, an absorbent layer impregnated with glycerine, and a layer of oelluloid adjacent the electrode.

3. An acoustic device of the condenser type comprising a stationary. electrode and a dia--v phragm having a conducting aluminium foil, an absorbentl layer impregnated -with glycerine, and a layer of collodion adjacent the electrode.

4. An acoustic device of the condenser type comprising a stationary electrode having openings therein, a conducting diaphragm overlying said electrode and a exible sheet interposed being a coating of -celluloid on the side in contact 10 with said stationary electrode.

EUGEN REISZ. 

